Method for producing metal microparticles

Abstract

Provided is a method for producing metal microparticles in which the ratio of crystallite diameter to the particle diameter of the metal microparticles is controlled. At least two types of fluid to be processed are used, including a metal fluid in which a metal or a metal compound is dissolved in a solvent, and a reducing agent fluid which includes a reducing agent. Sulfate ions are included in one or both of the metal fluid and the reducing agent fluid. The fluid to be processed is mixed in a thin film fluid formed between at least two processing surfaces, at least one of which rotates relative to the other, and which are disposed facing each other and capable of approaching and separating from each other, and metal microparticles are precipitated. The present invention is characterized in that at this time, the ratio (d/D) of the crystallite diameter (d) of the metal microparticles to the particle diameter (D) of the metal microparticles is controlled by controlling the molar ratio of metal and sulfate ions in the mixed fluid to be processed.

The invention claimed is: 
     
       1. A method for producing metal microparticle, wherein
 at least two fluids to be processed are used, 
 of these fluids to be processed, at least one fluid to be processed is a metal fluid in which a metal or a metal compound is dissolved in a solvent, 
 at least one fluid to be processed other than the said fluid to be processed is a reducing agent fluid which contains a reducing agent, 
 of these fluids to be processed, at least one fluid to be processed contains a sulfate ion, 
 the fluids to be processed are mixed to form a thin film fluid between at least two processing surfaces which are disposed in a position they are faced with each other so as to be able to approach to and separate from each other, at least one of which rotates relative to the other, whereby separating metal microparticle derived from the metal or the metal compound in the metal fluid, and 
 by increasing a molar ratio of the sulfate ion to the metal in the mixed fluid to be processed, a ratio (d/D) of a crystallite's diameter (d) of the metal microparticle to a particle diameter (D) of the metal microparticle is controlled to a range of 0.3 or more. 
 
     
     
       2. The method for producing metal microparticle according to  claim 1 , wherein of the fluids to be processed, at least one fluid to be processed contains a polyol. 
     
     
       3. The method for producing metal microparticle according to  claim 2 , wherein
 by increasing at least one of (a) concentration of the metal in the metal fluid, (b) concentration of the sulfate ion in the fluid to be processed before the mixing, and (c) mixing ratio of the fluids to be processed which are going to be mixed, the molar ratio of the metal and the sulfate ion in the mixed fluid to be processed is controlled to increase. 
 
     
     
       4. The method for producing metal microparticle according to  claim 2 , wherein
 the solvent is a polyol solvent. 
 
     
     
       5. The method for producing metal microparticle according to  claim 2 , wherein
 when executing the control, the ratio (d/D) of the crystallite's diameter (d) of the metal microparticle to a particle diameter (D) of the metal microparticle is controlled by controlling pH of the mixed fluid to be processed. 
 
     
     
       6. The method for producing metal microparticle according to  claim 2 , wherein
 when executing the control, the molar ratio of the sulfate ion in the metal fluid and/or the reducing agent fluid to the metal in the metal fluid is changed. 
 
     
     
       7. The method for producing metal microparticle according to  claim 1 , wherein
 by increasing at least one of (a) concentration of the metal in the metal fluid, (b) concentration of the sulfate ion in the fluid to be processed before the mixing, and (c) mixing ratio of the fluids to be processed which are going to be mixed, the molar ratio of the metal and the sulfate ion in the mixed fluid to be processed is controlled to increase. 
 
     
     
       8. The method for producing metal microparticle according to  claim 7 , wherein
 the solvent is a polyol solvent. 
 
     
     
       9. The method for producing metal microparticle according to  claim 7 , wherein
 when executing the control, the ratio (d/D) of the crystallite's diameter (d) of the metal microparticle to a particle diameter (D) of the metal microparticle is controlled by controlling pH of the mixed fluid to be processed. 
 
     
     
       10. The method for producing metal microparticle according to  claim 7 , wherein
 when executing the control, the molar ratio of the sulfate ion in the metal fluid and/or the reducing agent fluid to the metal in the metal fluid is changed. 
 
     
     
       11. The method for producing metal microparticle according to  claim 1 , wherein
 the solvent is a polyol solvent. 
 
     
     
       12. The method for producing metal microparticle according to  claim 11 , wherein
 when executing the control, the ratio (d/D) of the crystallite's diameter (d) of the metal microparticle to a particle diameter (D) of the metal microparticle is controlled by controlling pH of the mixed fluid to be processed. 
 
     
     
       13. The method for producing metal microparticle according to  claim 11 , wherein
 when executing the control, the molar ratio of the sulfate ion in the metal fluid and/or the reducing agent fluid to the metal in the metal fluid is changed. 
 
     
     
       14. The method for producing metal microparticle according to  claim 1 , wherein
 when executing the control, the ratio (d/D) of the crystallite's diameter (d) of the metal microparticle to a particle diameter (D) of the metal microparticle is controlled by controlling pH of the mixed fluid to be processed. 
 
     
     
       15. The method for producing metal microparticle according to  claim 14 , wherein
 when executing the control, pH of the metal fluid and/or the reducing agent fluid which is introduced into between the at least two processing surfaces is controlled in such a way that the said pH is constant under an acidic condition. 
 
     
     
       16. The method for producing metal microparticle according to  claim 14 , wherein
 when executing the control, pH of the metal fluid and/or the reducing agent fluid which is introduced into between the at least two processing surfaces is changed under an acidic condition. 
 
     
     
       17. The method for producing metal microparticle according to  claim 1 , wherein
 when executing the control, the molar ratio of the sulfate ion in the metal fluid and/or the reducing agent fluid to the metal in the metal fluid is changed. 
 
     
     
       18. The method for producing metal microparticle according to  claim 1 , wherein
 the metal or the metal compound comprises at least one of nickel, silver, copper, a nickel compound, a silver compound, or a copper compound. 
 
     
     
       19. The method for producing metal microparticle according to  claim 1 , wherein
 a first processing surface and a second surface are provided as the at least two processing surfaces, 
 the fluids to be processed are introduced into between the first processing surface and the second processing surfaces, 
 by a pressure of the fluids to be processed, a force to move the first processing surface and the second processing surface in a direction to separate with each other is generated, 
 by this force, a space is kept between the first processing surface and the second processing surface, and 
 the fluids to be processed which pass through this space kept between the first processing surface and the second processing surface form the thin film fluid. 
 
     
     
       20. The method for producing metal microparticle according to  claim 1 , wherein
 one of the metal fluid and the reducing agent fluid passes through between the at least two processing surfaces while forming the thin film fluid, 
 a separate introduction path independent of the flow path through which the one of the metal fluid and the reducing agent fluid runs is arranged, 
 at least one opening leading to the separate introduction path is arranged in at least any one of the at least two processing surfaces, and 
 the other of the metal fluid and the reducing agent is introduced from the opening into between the at least two processing surfaces, whereby mixing the metal fluid and the reducing agent fluid to form the thin film fluid.